Catalytic acrylonitrile production



Oct 1966 c. R. CAMPBELL ETAL 3,280,168

CATALYTIC AGRYLONITRILE PRODUCTION Filed July 9, 1964 INVENTORS BYfilial 771. TM

ATTORNEY United States Patent O 3,280,168 CATALYTIC ACRYLONETRILEPRODUCTHON Charles R. Campbell, Marion J. Mathews HI, and John J. Hicks,J12, Pensacola, Fla., and John F. Giblnr, Decatur, Ala., assignors toMonsanto Company, St. Louis, Mo., a corporation of Delaware Filed July9, 1964, Ser. No. 381,434 6 Claims. (Cl. 260-4653) This inventionrelates to the production of acrylonitrile. More particularly, itrelates to the catalytic production of acrylonitrile frombis-cyanoethylether.

It is known that acrylonitrile can be electrohydrodimerized toadiponitrile. Ordinarily, the electrohydrodimerization takes place inthe cathode compartment of a dually compartmented electrolytic cell. Thetwo compartments, anode and cathode, are separated by an ion exchangemembrane. An aqueous mixture comprised of acrylonitrile and a quaternaryammonium salt is continuously fed to the cathode compartment. A solutionof a strong mineral acid, usually sulfuric, is circulated in the anodecompartment. As current flows through the cell, acrylonitrile isconverted to adiponitrile and a minor amount of byproducts, among whichis bis-cyanoethylether.

After electrohydrodimerization, the adiponitrile, byproducts andacrylonitrile contained in the eflluent from the cathode compartment areseparated from the quaternary ammonium salt by an extraction procedure.Acrylonitrile and propionitrile, a byproduct, are subsequently separatedfrom the adiponitrile by distillation in an acrylonitrile-propionitrilestripping column. The tails from this distillation procedure, comprisedof adiponitrile and impurities, such as 3-hydroxypropioni-trile andbis-cyanoethylether, are passed to a distillation train to obtain aproduct of a least 99 weight percent adiponitrile.

Bis-cyanoethylether produced in the electrohydrodimerization procedurerepresents a yield loss. Furthermore, biscyanoethylether is in partthermally decomposed to 3- hydroxypropionitrile and acrylonitrile in thedistillation train, thereby making the purification of adiponitrile moredifficult.

An object of the invention is to provide a process for catalyticallyproducing acrylonitrile from bis-cyanoethylether.

Further, it is an object of this invention to provide a process fordecomposing bis-cyanoethylether obtained as a by-product of theelectrohydrodirneric conversion of acrylonitrile to adiponitrile, thusincreasing the yield of adiponitrile electrohydrodimerized fromacrylonitrile.

Other objects will become apparent from the following descriptivematerial.

In general, the above objects are achieved in the provision of aprocedure for catalytically converting bis-cyanoethylether toacrylonitrile and 3-hydroxypropionitrile. A small quantity of alkalinecatalyst, preferably a quaternary ammonium hydroxide, is intimatelycontacted with bis-cyanoethylether. The catalyst andbis-cyanoethylethylether mixture is then heated to decompose thebis-cyanoethylether to acrylonitrile and 3-hydroxypropionitrile.

To be more specific, a process is provided for catalytically convertingto acrylonitrile and 3-hydroxypropionitrile the bis-cyanoethylethercontained in a stream comprised of acrylonitrile, adiponitrile,propionitrile, bis-cyanoethylether, and 3-hydrox"'" nionitrile. Theprocess, basically, comprises heating tnc )am in the presence of analkaline catalyst, preferably a quaternary ammonium hydroxide.

It has been discovered that when the pH of the catholyte from theelectrohydrodimerization of acrylonitrile to adiponitrile is alkaline, aportion of the bis-cyanoethylether contained therein decomposes atelevated temperatures to form 3-hydroxypropionitrile and acrylonitrile.

ICC

On evaluation of various alkaline compounds including potassiumhydroxide, tetrabutylammoniurn hydroxide and tetramethylammoniumhydroxide, one finds that any suitable strong base catalyzes thedecomposition of bis-cyanoethylether. Quaternary ammonium hydroxidecompounds are preferred because they decompose at elevated temperaturesto form trialkyl amines and a monohydroxy alcohol or alkene, all ofwhich can be separated from the adiponitrile by distillation. Metallicbases do not decompose as readily as do organic bases; thus, they remainin the crude adiponitrile as it is further purified in the hereinbeforenoted distillation train. Distillation in the presence of a metallicbase tends to increase the hydrolysis of adiponitrile and the formationof 2-cyanocylopentylideneimine.

Alkaline catalyst concentration can vary over a rather wide range. Acatalyst concentration of about one (1) percent based on the weight ofbis-cyanoethylether substantially decomposes the bis-cyanoethylethercontained in the feed to the distillation zone wherein acrylonitrile andpropionitrile are separated from said feed. One-tenth (0.10) of onepercent alkaline catalyst based on the weight of bis-cyanoethylethercontatined in the feed mentioned next above decomposes about Weightpercent of the bis-cyanoethylether. As low as one (1) part per millionalkaline catalyst, based on the weight of the entire feed to theacrylonitrile-propionitrile stripping column, decomposes a substantialportion of the bis-cyanoethylether contained therein.

The drawing is a schematic flow diagram illustrating a specificembodiment of the invention.

To aid in further describing the invention, reference will now be madeto the drawing. The drawing illustrates a convenient point in theadiponitrile separation and purification procedure where catalyticdecomposition of biscyanoethylether can take place. The systemrepresented in the drawing is a distillation column whereinacrylonitrile and propionitrile are stripped from a stripper feedsimilar to that described in Table I below.

This column is preferably operated at about atmospheric pressure.Decomposition of bis-cyanoethylether can be accomplished at belowatmospheric pressure; but, condensation and recovery of acrylonitrile ismore difficult. This column is a convenient point to decomposebiscyanoethylether, for one of its basic functions is to strip awayacrylonitrile. It follows that at this point in the acrylonitrilerecovery process very little new equipment would be necessary topractice the invention.

Decomposition of bis-cyanoethylether could take place at other points inthe process for separation and purification of adiponitrile. However,they would not be nearly as convenient as the point or localeillustrated.

Stripper feed is fed to stripper 18 through line 10. Prior to enteringthe column a small quantity of an alkaline catalyst, for descriptivepurposes hereinafter restricted to quaternary ammonium hydroxide, ismetered from reservoir 12 through line 14 to feed line 10. It is to benoted that catalyst could also be metered into the column itself ratherthan the feed line. A typical stripper feed is set forth in thefollowing table.

TABLE I.TYPICAL STRIPPER FEED COMPOSITION 1 Principally 4-cyauosuberonitrlle 2 Principally suecinonltrile, cyanocyelopentylideneimine,cyanovaleramlde, and cyanovalerlc acid.

Feed is introduced near the top of column 18. This column is operated atsubstantially atmospheric pressure and customarily has a basetemperature from 200 to 220 C. The temperature across the column varies,i.e., the base temperature is greater than at the top. The basetemperature of the column can range from 150 to 250 C.Bis-cyanoethylether is catalytically decomposed to acrylonitrile and3-hydroxypropionitrile. Trialkylamine, monohydroxy alcohol or alkene,catalytically produced acrylonitrile, acrylonitrile already present inthe feed, water and propionitrile are distilled overhead through line20. After condensation the overhead stream separates in decanter 22 toproduce an organic and an aqueous layer. The organic layer, comprised ofacrylonitrile, propionitrile and water, is withdrawn through line 30.The aqueous layer, comprised of Water and a minor quantity ofacrylonitrile, is withdrawn from decanter 22 by means of line 24. Aportion of the aqueous layer is recycled as reflux to column 18 via line26 while the remainder flows by way of line 28 to an acrylonitrilerecovery distillation column. A tails stream of crude adiponitriletreated in accordance with the invention is withdrawn from column 18 vialine 32. This tails stream has a typical composition as shown in thefollowing table.

TABLE IL-TYPICAL STRIPPER TAILS COMPOSITION With 13 ppm.tetramethylamrnonium hydroxide added to feed Component:

Acrylonitrile 0.30 3-iydroxypropionitrile 3 .49 Z-meth-ylglutaronitrile0.3 2

Adiponitrile 90.75

High boilers 1 3.66 2-cyan0cyclopentylideneirnine 0.3 8 Cyanovalericacid 0.39 Bis-cyanoethylether 0.17

1 High boilers are primarily d cyanosuberonitrile and other highermolecular weight acrylonitrile oligomers.

cent concentration of tetramethylammonium hydroxide therein were chargedto a 100 ml. round-bottom flask equipped with a thermometer well. Thisflask was fitted with a heating mantle, distilling head, condenser, andreceiver. The flask was heated until the temperature reached 124 C. atwhich point material began to distill overhead. The temperature of theflask was increased over a four-minute period to 150 C. at the end ofwhich it was cooled to room temperature. Condensate distilled overheadweighed 6.24 grams and contained 5.99 grams (96%) acrylonitrile. Thisexperiment demonstrates that bis-cyanoethylether can be decomposedefiectively in the presencee of an alkaline catalyst to produceacrylonitrile.

Example II A series of continuous distillations were performed in whichfeed of a composition shown in Table III was introduced onto the toptray of a lO-tray, 2-inch Oldershaw column. The still was mounted on anelectrically heated reboiler having a weir arrangement for continuouswithdrawal of still tails. Overhead vapors were condensed in a glasscondenser and the condensate flowed to a decanter wherein an upper layercontaining acrylonitrile, propionitrile, and water was separated from alower aqueous layer containing about 7 weight percent acrylonitrile.

Feed was pumped to the column at the rate of 1,675 grams per hour. Theaqueous, lower layer from the decanter was returned to the top of thecolumn as reflux at 360 grams per hour. The residence time of the tailsin the reboiler at a tails withdrawal rate of 360 grams per hour was 2hours. The reboiler temperature was maintained at 200-210 C. while thehead temperature ranged from 80 to 85 C.

A series of runs was performed employing the above operating conditionsand using various catalysts and catalyst concentrations; in one of theruns no alkaline catalyst was added to the feed. Table HI summarizes theruns. Compositions are given in weight percent.

TABLE III-SUMMARY OF RUNS EMPLOYING ALKALINE CATALYSTS TO DECOMPOSEBIS-CYANOETHYLETHE R.

Composition of Tails Stream Composition Component of Feed Strem With NoWith 13 p.p.m. With 310 p.p.m. With 130 p.p.m.

Catalyst TMAOI-I 2 TBAOH KOH 4 Added to Feed Added to Feed Added to FeedAcrylonitrilo, percent i, 73. 84 0. 25 30 0.23 0.14 Propionitrile,percent 5. 43 3-Hydroxypr0pionitrile,

percent O. 20 2. 75 3. 49 1. 0. 64 Z-methylglutaronitrile,

percent 0. 11 0. 58 .32 0. 40 0. 53 Adiponitrile, percent 18. 00 86. 839 .75 93. 20 92. 57 High Boilers percen 0. 85 3. 29 3. 6 2. 98 3. 95 2eyauocyclopentyllden imine, percent 0. O1 0. 31 38 0. D6 0. 21Cyanovalerie Acid,

percent 0. l8 0. 32 39 0. 85 0. 53 B is-cyanoethylether,

percent 1. 30 4. 93 0. l7 0. 00 0. 00

1 High boilers are primarily cyariosuberonitrile and other highermolecular weight aerylonitrile oligomers 2 TMAOH is tetramethylammoniumhydroxide. 3 TBAOH is tetrabutylammonium hydroxide.

4 KOH is potassium hydroxide.

The following examples are set forth to illustrate the invention. Theyare intended to elucidate and are not intended to be limiting in anyway.

Example I Twenty-five (25) grams of bis-cyanoethylether and one (1) gramof an aqueous solution having a 25 weight perproduced fromacrylonitrile. Furthermore, a process is provided for the effectiveremoval of bis-cyanoethylether from the crude adiponitrile prior to itsentering the adiponitrile purifying distillation train.

Although the invention has been described by reference to specificembodiments, it should be broadly construed and should be limited onlyto the scope of the claims appended hereto.

We claim:

1. A continuous process for producing acrylonitrile frombis-cyanoethylether produced as a by-product in theelectrohydrodimerization of acrylonitrile to adiponithe heated zonecontains at least 1 part per million alkaline catalyst based on theweight of the stream.

3. The process of claim 1 wherein the highest tem perature in the heatedzone is between and 250 C.

4. The process of claim 1 wherein the distillation is performed atsubstantially atmospheric pressure.

5. The process of claim 1 wherein the alkaline catalyst is a quaternaryammonium hydroxide.

6. The method of claim 1 wherein the quaternary ammonium hydroxide istetramethylammonium hydroxide.

References Cited by the Examiner UNITED STATES PATENTS 2,382,036 8/1945Bruson 260465.6 2,448,979 9/1948 Hopff et al 260465.6 2,770,640 11/1956Journeay 260465.9 X-R 2,790,818 4/1957 Journeay 260465.9 XR 2,816,13012/1957 Selcer et a1. 260465.6 2,832,798 4/1958 Rapoport 260465.93,024,267 3/ 1962 Howsman 260465 .6

CHARLES B. PARKER, Primary Examiner.

JOSEPH P. BRUST, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,280,168 October 18, 1966 Charles R. Campbell et ale It is herebycertified that error appears in the above numbered patent requiringcorrection and that the said Letters Patent should read as correctedbelow.

Column 1, line 64, the indistinct word should readS-hydroxypropionitrile line 65, the indistinct words should read thestream Signed and sealed this 5th day of September 1967! L) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner ofPatents

1. A CONTINUOUS PROCESS FOR PRODUCING ACRYLONITRILE FROMBIS-CYANOETHYLETHER PRODUCED AS A BY-PRODUCT IN THEELECTROHYDRODIMERIZATION OF ACRYLONITRILE TO ADIPONITRILE COMPRISING THESTEPS OF: (A) METERING A MINOR QUANTITY OF AN ALKALINE CATALYST SELECTEDFROM THE GROUP CONSISTING OF QUATERNARY AMMONIUM HYDROXIDE AND POTASSIUMHYDROXIDE INTO A STREAM COMPRISED OF ACRYLONITRILE, ADIPONITRILE,PROPIONITRILE, BIS-CYANOETHYLETHER, AND 3-HYDROXYPROPIONITRILE; (B)FEEDING SAID STREAM HAVING ALKALINE CATALYST THEREIN INTO A ZONE BETWEEN70 AND 250*C.; AND (C) DISTILLING SAID STREAM TO REMOVE ACRYLONITRILEAND PROPIONITRILE THEREFROM.